UNDERSTANDING THE TECTONIC EVOLUTION OF THE WEST ORPHAN BASIN, OFFSHORE CANADA, AND THE CONJUGATE ROCKALL BASIN, OFFSHORE IRELAND, USING A SEISMIC MEGATRANSECT by © Heide M. MacMahon A Thesis submitted to the School of Graduate Studies in partial fulfilment of the requirements for the degree of Master of Science/Earth Science/Geophysics Memorial University of Newfoundland May 2019 St. John’s Newfoundland and Labrador Abstract The Orphan Basin, offshore Newfoundland, Canada, is approximately conjugate to the rifted margin basins on the Irish Atlantic margin. At the onset of seafloor spreading, plate reconstructions, based solely on oceanic magnetic anomalies, show the Rockall Basin, west of Ireland, forming a continuous Mesozoic basin with the West Orphan Basin. Here, the nature of this potentially continuous basin is examined through the development of a Newfoundland- Ireland conjugate basins model. 2D and 3D reconstructions of the West Orphan and Rockall basins yielded the thickness of the post-rift and syn-rift sedimentary packages, as well as the pre-rift crust. A discrepancy inspired additional analysis of the East Orphan Basin to aid in the reconstruction of the continuous Mesozoic basins. Based on the results of the reconstruction of the East Orphan Basin, it is possible that the Rockall Basin was originally conjugate to, and continuous with, the East Orphan Basin. ii Acknowledgments I would like to begin by thanking my supervisor Kim Welford for taking me on as a willing graduate student, for providing me this project and for facilitating the data access required for this project. I would also like to thank you for being the kind and welcoming supervisor that you are, I truly appreciate everything you have done for me. I would also like to thank Luke Beranek for his insightful comments as a committee member. I would like to thank the Petroleum Affairs Division of the Department of Communications, Climate Action and Environment, of the Irish government for generously providing the Rockall Basin and Porcupine Basin 2D seismic data set. I would also like to thank TGS for providing the Orphan Basin 2D seismic data set. Thank you to the Canada- Newfoundland and Labrador Offshore Petroleum Board (C-NLOPB) for providing additional geological and geophysical well logs within the Orphan Basin. Additionally, thank you to Innovate NL for funding this project. Another big thank you to Larry Sandoval for your help during this process, and indulging every question I had regarding Petrel. Thank you to Alex Peace for your structural knowledge and overall thesis advice. A big thank you to Stuart Smith, the senior support geologist at Move©, for his speedy and insightful help and without whom this project would have taken twice as long. I would also like to thank Mohamed Gouiza for his useful insights and numerous email correspondences. A special thank you to my family for all their support, especially my mother, Susanne. Your constructive criticism and speedy edits pushed me forward every day. Your love and support has never gone unnoticed or unappreciated. Thank you for being a strong, independent female role iii model in my life. Finally, to my boyfriend, Bill Clarke, thank you for your unwavering belief, never ending support and your unconditional love. iv Dedication This thesis is dedicated to my incredible mother, Susanne MacMahon You are strong and passionate, You are smart and brave, You are my inspiration. I could not have done this without you. I love you. v Table of Contents Title Page i Abstract ii Acknowledgements iii Dedication v Table of Contents vi List of Tables ix List of Figures x Chapter 1: Introduction 1.1 Classification of Rifted Margins 2 1.2 The Newfoundland-Ireland Conjugate Margins 7 1.2.1 Introduction to the Rockall Basin 7 1.2.2 Introduction to the Orphan Basin 10 1.3 Basin Evolution 13 1.3.1 Rockall Basin 13 1.3.2 Orphan Basin 15 1.4 Past Work 17 1.4.1 Rockall Basin 17 1.4.2 Orphan Basin 23 1.5 Purpose 28 1.6 Thesis Outline 29 Chapter 2: Data and Methods 2.1 Data 30 2.1.1 Rockall Basin 31 2.1.2 Orphan Basin 34 2.2 Methods 36 2.2.1 Petrel© Seismic Analysis 36 2.2.2 Move© Model Restoration 36 2.2.2.1 2D Depth Conversion 36 2.2.2.2 2D Decompaction 39 2.2.2.3 2D Thermal Subsidence 41 vi 2.2.2.4 2D Fault Restoration 43 Chapter 3: Seismic Interpretation 3.1 Introduction 45 3.2 Rockall Basin 45 3.2.1 Seismic Stratigraphy 48 3.2.1.1 Cenozoic 48 3.2.1.2 Upper Cretaceous 50 3.2.1.3 Lower Cretaceous 52 3.2.1.4 Acoustic Basement 55 3.3 Orphan Basin 57 3.3.1 Seismic Stratigraphy 57 3.3.1.1 Cenozoic 59 3.3.1.2 Upper Cretaceous 60 3.3.1.3 Lower Cretaceous 62 3.3.1.4 Jurassic 63 3.3.1.5 Acoustic Basement 65 3.4 From Seismic Interpretation to Modelling 67 © Chapter 4: Basin Modelling in Move 4.1 Introduction 68 4.2 2D Modelling 68 4.2.1 Time to Depth Conversion 68 4.2.2. Cenozoic Sedimentary Rock Decompaction 73 4.2.3 Cenozoic Thermal Subsidence Restoration 74 4.2.4 Upper Cretaceous Sedimentary Rock Decompaction 77 4.2.5 Upper Cretaceous Thermal Subsidence Restoration 79 4.2.6 Lower Cretaceous Decompaction 80 4.2.7 Jurassic Sedimentary Rock Decompaction 81 4.2.8 Jurassic Fault Restoration and Unfolding 83 4.2.9 Upper Crustal Decompaction 84 4.2.10 Crustal Fault Restoration and Unfolding 86 4.3 3D Modelling 88 4.3.1 Present Day 89 vii 4.3.2 Cenozoic Decompaction and Thermal Subsidence 91 4.3.3 Upper Cretaceous Decompaction and Thermal Subsidence 93 4.3.4 Lower Cretaceous Decompaction 95 4.3.5 Jurassic Decompaction and Fault Restoration 98 4.3.6 Upper Crust Decompaction and Fault Restoration 100 4.4 From Modelling to Broader Understanding 100 Chapter 5: Discussion 5.1 Introduction 102 5.2 Orientation of Restored Seismic Lines with Respect to Orientation of Rifting 103 5.3 Variable vs. Uniform Stretching Factor, Beta Values in the West Orphan Basin 103 5.4 Interpreted Jurassic Sedimentary Rocks (or lack thereof) 107 5.4.1 Orphan Basin 107 5.4.2 Rockall Basin 110 5.5 Nature of Faulting Across the Rockall and Orphan Basins 113 5.6 Sedimentary Rock Thickness 117 5.7 Amount of Extension 118 5.8 Continental Crustal Thickness 121 5.9 Effects of Inherited Crustal Structures 122 5.10 Igneous Intrusions 123 5.11 Partial Serpentinization of the Mantle 130 5.12 Crustal Boudinage of the Newfoundland-Ireland Conjugate Margins 133 5.13 Previously Published Plate Reconstructions 135 5.13.1 Previously Published Plate Reconstructions Determined from Magmatic Events 141 5.14 Comparison of East Orphan Basin and Rockall Basin 143 Chapter 6: Conclusions and Future Work 6.1 Conclusions 152 6.2 Future Work 156 References 158 Appendix A 169 viii List of Tables 2.1 Density and velocity parameters for each layer for the West Orphan Basin and the Rockall Basins 38 2.2 Rifting time-table for the West Orphan Basin and the Rockall Basin, used for 2D Thermal Subsidence calculations 43 5.1 Average thicknesses of the pre-rift crust, the syn-rift sedimentary rock and the post-rift sedimentary rock in the West and East Orphan basins and the Rockall Basin. 151 ix List of Figures (Abbreviated Titles) 1.1 Image of the North Atlantic margin 2 1.2 Schematic illustration showing the important steps in the progressive extension of the lithosphere leading to continental break-up (Reston, 2007a) 5 1.3 Schematic illustration showing the important steps in the progressive extension of the lithosphere leading to continental break-up (Reston, 2007a) 6 1.4 Location of the Rockall Basin, offshore Ireland, location of vintage seismic lines and current seismic lines for this thesis 8 1.5 Free air gravity anomaly map of the Rockall Basin 9 1.6 Location of the Orphan Basin, Offshore Newfoundland, location of vintage seismic lines and current seismic lines for this thesis 11 1.7 Free air gravity anomaly map of the Orphan Basin 12 1.8 Two wave travel time profile of the Rockall slope and basin (England & Hobbs 1997) 18 1.9 Cross-section models from Ireland to the Iceland Basin (Shannon et al., 1999) 20 1.10 Deep structure beneath a seismic profile in the Rockall Basin, including gravity model (Kimbell et al., 2010) 22 1.11 Final velocity model from across the entire stretched continental crust of the Rockall Basin, with observed and computed gravity anomalies (Chian et al., 2001) 25 1.12 Depth to basement reconstruction across both the Newfoundland and Irish Atlantic conjugate basins (Welford et al., 2012) 26 1.13 Geological interpretation of depth section Or0–122, in the Orphan Basin (Lau et al., 2015) 27 1.14 Structural comparison between the Orphan Basin and its European counterparts From Lau et al. (2015). (a) Rockall Trough (Morewood et al., 2005). (b) Porcupine Basin (O’Reilly et al., 2006). (c) Orphan Basin (Lau et al., 2015) 28 2.1 All Irish Atlantic seismic and well data provided by the Irish Government 31 2.2 A cross-section of the younger Rockall Basin and the older perched basins, the Erris Basin and the Donegal Basin. This figure was adapted from Corfield et al. (1999) 32 x 2.3 Polygons showing the age of basins in the Irish North Atlantic 33 2.4 Location of all the seismic lines provided by TGS 35 3.1 (A) Map of offshore Ireland, showing the location of seismic lines IR1 and IR2 in the Rockall Basin.